System and method of producing a composite product

ABSTRACT

A method of producing a composite product is provided. The method includes providing a fluidized bed of carbon-based particles in a fluidized bed reactor, providing a catalyst or catalyst precursor in the fluidized bed reactor, providing a carbon source in the fluidized bed reactor for growing carbon nanotubes, growing carbon nanotubes in a carbon nanotube growth zone of the fluidized bed reactor, and collecting a composite product comprising carbon-based particles and carbon nanotubes.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/308,496, filed Mar. 15, 2016, which is incorporated herein by reference in its entirety.

BACKGROUND

The field of the present disclosure relates generally to carbon nanotubes and, more specifically, to systems and methods of producing composite products including carbon nanotubes.

Carbon nanotubes are small tube-shaped structures essentially having a composition of a graphite sheet in a tubular form. Carbon nanotubes feature diameters less than 100 nanometers, and large aspect ratios, where the length is much greater than is the diameter. For example, a length of the CNT may be more than 1000 times the diameter. Single-walled carbon nanotubes (SWNT) are increasingly becoming of interest for various applications in nanotechnology because of their unique electronic structures, which gives them exceptional thermal, mechanical, and electrical properties. For example, SWNTs can be used in electronics, energy devices, medicine, and composite materials in order to obtain desirable physical and chemical properties. These uses require methods for producing significant quantities of SWNTs.

Processes for producing SWNTs include, but are not limited to, physical methods (e.g., electrical arc, laser ablation) and chemical methods (e.g., pyrolysis, chemical vapor deposition). Once formed, the SWNTs are sometimes distributed within a matrix material, which modifies the thermal, mechanical, and electrical properties of the matrix material. However, the enhancement of electrical or mechanical properties of matrix material by nanotube additives requires very homogeneous dispersion, no agglomeration and fine control over the nanotube/matrix ratios. Attempts have been made following the synthesis of nanotubes to disperse the nanotubes in various solvents (e.g. via surface functionalization) followed by mixing of the nanotubes with the matrix (e.g. by ball milling, sonication etc.). However, such attempts have failed to provide satisfactory dispersion of the nanotubes in the matrix.

BRIEF DESCRIPTION

In an aspect, a method of producing a composite product is provided. The method includes fluidizing an amount of carbon-based particles within a fluidized bed reactor, providing a catalyst or catalyst precursor in the fluidized bed reactor, providing a carbon source to a carbon nanotube growth zone of the fluidized bed reactor, growing carbon nanotubes in the carbon nanotube growth zone, and providing a flow of carrier gas to the fluidized bed reactor and carrying a composite product comprising carbon nanotubes and carbon-based particles through the fluidized bed reactor.

In an aspect, a system for use in producing a composite product is provided. The system includes a fluidized bed reactor comprising an amount of carbon-based particles contained therein, an outlet, a catalyst or catalyst precursor source in fluid communication with the fluidized bed reactor to provide a flow of catalyst or catalyst precursor in the fluidized bed reactor, and a carrier gas source in fluid communication with the fluidized bed reactor to carry a composite product comprising carbon-based particles and carbon nanotubes grown in the fluidized bed reactor.

In an aspect, a method of producing a composite product is provided. The method includes providing a fluidized bed of carbon-based particles in a fluidized bed reactor, providing a catalyst or catalyst precursor in the fluidized bed reactor, providing a carbon source in the fluidized bed reactor for growing carbon nanotubes, growing carbon nanotubes in a carbon nanotube growth zone of the fluidized bed reactor, and collecting a composite product comprising carbon-based particles and carbon nanotubes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary system that may be used to produce a composite product in an aspect of the disclosure.

FIG. 2 a flow diagram illustrating an exemplary series of process steps that may be used in producing a composite product in an aspect of the disclosure.

DETAILED DESCRIPTION

The embodiments described herein relate to a composite product, and systems and methods for making the composite product. In general, the systems and methods provide for the in-situ dispersion of carbon nanotubes into a carbon-based matrix material in the course of carbon nanotube growth in a reactor. The reactor may be a fluidized bed reactor capable of aerosolization or fluidization of the carbon-based matrix material with a fluidization gas flowing from a gas distributor, such as a porous frit, from the bottom of the reactor. One or more injectors may be provided in the middle of the reactor to supply catalyst and carbon precursors for growing of the carbon nanotubes. Hence, carbon nanotubes may be grown in a cloud of fluidized carbon matrix material to provide in-situ mixing and, as a result, improved homogeneity of the resulting composite product containing the carbon nanotubes and carbon-based matrix material.

FIG. 1 is a schematic illustration of an exemplary system 100 that may be used to produce a composite product 102 comprising carbon nanotubes and carbon-based matrix materials. In the exemplary embodiment, system 100 includes a fluidized bed reactor 104 having an amount of carbon-based matrix material contained therein. The matrix material may be any solid, carbon-based particle that is capable of being suspended in a fluidized bed. An exemplary carbon-based particle includes, but is not limited to, graphite particles, graphite flakes, and combinations thereof. For example, the carbon-based particles can have a particle size defined within a range between about 1 nanometer and about 100 microns.

In an illustrative example, the fluidized bed reactor 104 includes a reaction chamber 108, and a gas distributor that may comprise a porous frit 110 coupled to reaction chamber 108 and a gas plenum 112 coupled to porous frit 110. Porous frit 110 includes a plurality of flow apertures 114 defined therein such that gas plenum 112 is coupled in fluid communication with reaction chamber 108. Gas plenum 112 receives a flow of fluidizing gas from a first gas source 118. The flow of fluidizing gas is routed through plenum 112 and the porous frit 110 to fluidize the carbon-based particles in the reaction chamber 108. The fluidizing gas may be any gas capable of fluidizing the carbon-based particles to form a fluidized bed 109 of carbon-based particles. Exemplary fluidizing gases include, but are not limited to, argon, helium, nitrogen, hydrogen, carbon dioxide, and ammonia.

As shown in FIG. 1, the fluidized bed reactor 104 may include one or more heat sources 119 for heating the reaction chamber 108 to the desired reaction temperature. For example, the reaction chamber 108 may be heated with the heat source 119 to a temperature in the range of about 450° C. to about 1100° C. depending on the catalyst or catalyst precursor and the type of nanotube desired. Typically, single-walled nanotubes (SWNTs) require higher temperatures (>750° C.) while multi-walled nanotubes (MWNTs) can be grown as low as about 450° C.

Fluidized bed reactor 104 may also include one or more inlets for introduction of the carbon-based particles, the catalyst or catalyst precursor, a carrier gas, and the carbon precursor for the carbon nanotubes. As shown in FIG. 1, an inlet 120 is provided for the introduction of the carbon-based particles from a carbon-based particle source 106 into the reaction chamber 108. It is to be understood that any method or device may be used to introduce the carbon-based particles into the reaction chamber 108 via the inlet 120. In a non-limiting example, the carbon-based particles may be fed into the reaction chamber 108 with a screw feeder, belt feeder, vibratory feeder, or a rotary (bulk solid) feeder. In addition, or alternatively, the carbon-based particles may be conveyed pneumatically into the reaction chamber 108. Non-limiting examples include pressure vessel conveyors, pressurized screw conveyor, airlifts, blow-through feeders, and jet feeders. The conveying gas may the same as or different than the fluidizing gas. Exemplary gases include, but are not limited to, argon, nitrogen, helium, hydrogen, carbon dioxide, and ammonia. It is to be understood that the carbon-based particles may be continuously fed into the reaction chamber 108 so that the system operates in a continuous operation of the reaction chamber 108, the carbon-based particles may be introduced in a single charge for batch operation of the reaction chamber 108, or the carbon-based particles may be intermittently added for semi-batch operation of the reaction chamber 108.

The carbon nanotubes can be synthesized using carbon precursors, such as one or more carbon-containing gases, one or more hydrocarbon solvents, and mixtures thereof. Examples of carbon-containing precursors include carbon monoxide, aliphatic hydrocarbons, both saturated and unsaturated, such as methane, ethane, propane, butane, pentane, hexane, ethylene, acetylene and propylene; oxygenated hydrocarbons such as acetone, and methanol; aromatic hydrocarbons such as benzene, toluene, and naphthalene; and mixtures of the above, for example carbon monoxide and methane. In general, the use of acetylene promotes formation of multi-walled carbon nanotubes, while CO and methane are preferred feed gases for formation of single-walled carbon nanotubes. Specifically, hydrocarbon solvents may include, but are not limited to, alcohols such as methanol, ethanol, and isopropanol. The carbon precursor may optionally be mixed with a diluent gas such as hydrogen, helium, argon, neon, krypton and xenon or a mixture thereof. As shown in FIG. 1, a carbon precursor may be included in a carrier gas (carrier gas source 126) and introduced to the reaction chamber 108 via inlet 128.

The catalyst or catalyst precursors may include any catalyst or catalyst precursor that may be used in the production of carbon nanotubes. The catalyst or catalyst precursor may be one or more of an acetylacetonate, a metallocene, an acetate, a nitrate, a nitride, a sulfate, a sulfide, an oxide, a halide, a chloride, and the like. Illustrative metals for use as the catalyst include, but are not limited to, iron, nickel, cobalt, molybdenum, or a mixture thereof. Non-limiting examples of catalyst precursors include Iron(III) acetylacetonate, ferrocene, iron acetate, iron nitrate, iron sulfate, and iron chloride. It is to be understood that the catalyst or catalyst precursor source may be a solid powder, a solid dispersed in a liquid, or dissolved in a solvent. As shown in FIG. 1, a catalyst or catalyst precursor source 130 may be provided in communication with the reaction chamber 108 via inlet 132 to introduce the catalyst or catalyst precursor to a carbon nanotube growth zone 150 of the reaction chamber 108. A pump, solids feeder, syringe, or any other device or method known to one of ordinary skill in the art may be used to introduce the catalyst or catalyst precursor into the carbon nanotube growth zone 150. It is to be understood that the carbon precursor may be mixed with the catalyst or catalyst precursor and introduced with the catalyst or catalyst precursor via inlet 132.

In a non-limiting example, the carbon-based particles can be provided with a catalyst or catalyst precursor deposited thereon prior to introduction of the carbon-based particles in the reaction chamber 108.

In operation, the growth rate of carbon nanotubes and the weight percentage of carbon nanotubes relative to the carbon-based particles in the composite product is controlled by the feed rates of the carbon-based particles, the catalyst or catalyst precursor, and the carbon precursor into the reaction chamber 108. These feed rates can be tailored to produce the desired ratio of carbon nanotubes to carbon-based particles in the composite product to meet the needs of a desired application.

In an illustrative example as shown in FIG. 2, a method of making the composite product comprises providing a fluidized bed of a carbon-based particles (step 200), providing a catalyst or catalyst precursor in the fluidized bed (step 300), introducing a carbon source in the fluidized bed (step 400), growing carbon nanotubes in the fluidized bed (step 500), and collecting the composite product comprising carbon-based particles and carbon nanotubes (step 600). In a non-limiting example, at least some of the catalyst or catalyst precursor is deposited on the surface of the carbon-based particles and the carbon nanotubes are grown on the surface of the carbon-based particles.

EXAMPLE Production of Composite Product

To demonstrate the method of producing a composite product comprising carbon nanotubes and carbon-based solids, the following experiment was conducted.

A quartz tube having a 2 inch diameter was provided as the reaction chamber 108 for the fluidized bed reactor 104 and a tube furnace was used as the heat source 119. The quartz tube was aligned vertically with a lower end closed with the porous frit 114. Two tubes were provided at the center of the porous frit 114 for the carrier gas inlet 128 and the catalyst/catalyst precursor inlet 132. Both inlets 128/132 were positioned below the section of the reaction chamber 108 heated by the heat source 119. Graphite particles were used as the carbon-based particles and were poured onto the porous frit 114 to a height of about 10 millimeters. The fluidizing gas, argon, was then provided at a rate of about 350 sccm (standard cubic centimeters per minute) through the porous frit 114 at the lower end of the quartz tube to fluidize the graphite particles. The reactor chamber 108 was heated to a temperature of about 1020° C. The carrier gas included a mixture of argon (about 850 sccm) and hydrogen (about 300 sccm) and was provided to the reaction chamber 108 via inlet 128. The catalyst precursor was a solution of ferrocene (0.4 wt %) and thiophene (0.2 wt %) in ethanol. The ethanol functioned as both a solvent for the ferrocene and the carbon source for growing the nanotubes. The catalyst precursor solution was injected at a rate of 6 ml/hr via the inlet 132 into the carbon nanotube growth zone 150 where the ferrocene decomposed to iron catalyst particles having a diameter of about one nanometer, and the ethanol was converted to a carbon source for the growth of single walled nanotubes on the iron catalyst particles. The carrier gas transported the composite product 102 from the nanotube growth zone 150 through the reactor outlet 175 and to the collection vessel 170. The composite product included SWCNTs and graphite particles and comprised approximately 0.7 wt % SWCNTs.

This written description uses examples to disclose various implementations, including the best mode, and also to enable any person skilled in the art to practice the various implementations, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 

What is claimed is:
 1. A method of producing a composite product, said method comprising: a) within a fluidized bed reactor: separately fluidizing an amount of carbon-based particles and a catalyst or catalyst precursor in the presence of a carbon source; b) after a), growing carbon nanotubes in a carbon nanotube growth zone of the fluidized bed reactor; and c) providing a flow of carrier gas to the fluidized bed reactor and carrying a composite product comprising the carbon nanotubes and the carbon-based particles through the fluidized bed reactor.
 2. The method in accordance with claim 1, wherein carrying the composite product through the fluidized bed reactor comprises transporting the composite product towards an outlet defined near a top of the fluidized bed reactor.
 3. The method in accordance with claim 1, further comprising receiving the composite product discharged from the outlet of the fluidized bed reactor in a collection vessel.
 4. The method in accordance with claim 1, further comprising at least one of continuously or periodically replenishing the carbon-based particles in the fluidized bed reactor.
 5. The method in accordance with claim 1, further comprising heating the carbon nanotube growth zone to a temperature greater than about 1000° C.
 6. The method in accordance with claim 1, wherein fluidizing the catalyst or catalyst precursor comprises injecting the catalyst or catalyst precursor from a bottom portion of the fluidized bed reactor and into the nanotube growth zone.
 7. The method in accordance with claim 1, wherein providing the carrier gas comprises discharging a flow of the carrier gas into the nanotube growth zone and transporting the catalyst through the nanotube growth zone toward the fluidized bed reactor outlet.
 8. The method in accordance with claim 1, wherein the fluidized bed reactor comprises a gas distributor positioned below the nanotube growth zone, and fluidizing the carbon-based particles within the fluidized bed reactor comprises feeding a fluidizing gas through the gas distributor at a rate sufficient to fluidize the carbon-based particles within the fluidized bed reactor.
 9. The method in accordance with claim 1, wherein the carbon-based particles are graphite particles, and the carbon nanotubes are single-wall carbon nanotubes.
 10. The method according to claim 1, wherein the method is a continuous method.
 11. The method according to claim 1, wherein fluidizing the catalyst or catalyst precursor in the fluidized bed reactor comprises fluidizing the catalyst precursor in the fluidized bed reactor.
 12. The method according to claim 11, wherein the catalyst precursor comprises one selected from the group consisting of iron(III) acetylacetonate, ferrocene, iron acetate, iron nitrate, iron sulfate, iron chloride, and combinations thereof.
 13. The method according to claim 12, wherein the catalyst precursor further comprises an alcohol, and wherein the alcohol is the carbon source for growing the carbon nanotubes.
 14. The method according to claim 12, wherein the catalyst precursor comprises ferrocene.
 15. The method according to claim 14, wherein the catalyst precursor further comprises an alcohol, and wherein the alcohol is the carbon source for growing the carbon nanotubes.
 16. The method according to claim 1, wherein the catalyst comprises one selected from the group consisting of a solid powder, a solid dispersed in a liquid, a solid dissolved in a solvent, and combinations thereof.
 17. The method according to claim 1, wherein the catalyst or catalyst precursor and the carbon source are provided as a catalyst precursor solution. 